Changes
→Trivia
*The demo version was released after the game's release on March 4, 2000. It features portions of ''[[Welcome to Black Mesa]]'', ''[[Friendly Fire]]'' and ''[[Foxtrot Uniform]]'' with minor changes.
*If the player follows [[Gordon Freeman]] through the portal to [[Xen]] in ''[[We Are Not Alone]]'', the game will end, accusing the player of trying to rewrite the history with a game over message that says: "Evaluation terminated, Subject attempted to create a temporal paradox". This means what happened in the original level was changed by the player. It is possible to kill Gordon immediately after following him through the portal to Xen; after coming through the portal, Shephard must lob an assault rifle grenade onto Gordon's platform before falling to his death, which will cause Gordon to be 'gibbed' by the explosion. However, the paradox end message will still play regardless of this and the last save point will be loaded.
*This is the only game in the Half-Life series to feature night vision instead of the flashlight and the only one to have the rope-climbing mechanic.